Resting metabolic rate (RMR) appears to decline with age. This has important implications for optimal health and functional status, especially in the elderly. Previous efforts at understanding the relationship between this decline in metabolic rate and age are surrounded by technical and methodological limitations. The aim of this study.is to clarify the changes in resting metabolic rate that occur with aging using state-of-the-art methods. The objectives of the proposed study are to determine in 50-healthy Hispanic, weight stable women if; l) a reduction in RMR in relation to fat free mass (FFM) in the elderly is in part secondary to energy expenditure and body composition measurement techniques that are inappropriate for use or inaccurate in the elderly. 2) a reduction in RMR in relation to FFM in the elderly is in part related to a lowering of the proportion of FFM as body cell mass. The fraction of FFM as extracellular fluid according to this hypothesis is increased. 3) a reduction in RMR in the elderly is appropriate for the reduction in body cell mass. Subjects will be 25 young (18-25 yrs) and 25 elderly (70 yrs and above) Puerto Rican women. 'Since obesity and associated complications are common in the Hispanic community, a steadily growing minority group in the United States, this study proposes to address some of the clinical concerns that may contribute to these conditions.